Laser beam machining apparatus and laser beam machining method

ABSTRACT

A laser beam machining apparatus forms blind holes at predetermined intervals in a workpiece by intermittently irradiating a laser beam from a laser nozzle to the workpiece while the laser nozzle and the workpiece being moved relatively. During the time the workpiece is subjected to machining, the electrostatic capacity between the support member and the laser nozzle is detected by an electrostatic capacity sensor while the workpiece made of conductive material is supported on the support member. The irradiation output power is controlled by a control unit which operates to vary the number of output pulses from the laser nozzle each time one hole is formed according to the result detected in response to variation in the thickness of the workpiece.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a laser beam machining apparatusfor forming a tearable portion in a workpiece such as automotiveinstrument panel by irradiating a laser beam and a laser beam machiningmethod therefor.

[0003] 2. Description of the Related Art

[0004] Air bags for passenger seats of automobiles are generally placedon the inside of instrument panels. Moreover, an opening is formed inthe instrument panel in a position opposite to the air bag and a coverplate is mounted over the opening; or otherwise there is formed a groovefor use in cleaving a predetermined opening portion in the instrumentpanel though no opening is provided therein. In this case, the air bagis normally covered with the cover plate or the opening portion and whenthe air bag is activated, the cover plate is broken or the openingportion is cloven out of the groove so that the air bag is inflatedoutside the instrument panel.

[0005] With the above structure of covering the air bag, however, theproblem of spoiling the external appearance arises as the outward formof the cover plate or the groove of the opening portion is exposed onthe front surface of the instrument panel. A further problem is that thereflection of the outward form of the cover plate or the grooves of theopening portion on the front window also puts a restraint on drivingactivity.

[0006] In order to deal with the foregoing problems, there has beenproposed a method of forming a tearable portion by drilling blind holesat predetermined intervals in the rear side of an instrument panel toform a line of perforations. In this method, however, it is needed toform the tearable portion having a predetermined value of breakingstrength over the whole periphery while a predetermined remain thicknessis secured between the bottom face of each perforation and the frontsurface side of the panel.

[0007] Nevertheless, because instrument panels are curved and of uneventhickness when they are produced by molding, it has been difficult todrill blind holes in the instrument panel so that the remain thicknessis secured uniformly.

[0008] In order to deal with the problem above, there have heretoforebeen proposed laser beam machining methods as disclosed in, for example,Japanese Patent Laid-Open No. 85966/1998 (the first prior art) andJapanese Patent Laid-Open No. 2001-38479 (the second prior art).

[0009] According to the first prior art, when a tearable portion as ablind hole is drilled by the irradiation of a laser beam to a workpiece,the laser beam transmitted through the aperture is detected whereby tostop the drilling of the aperture when the power transmittedtherethrough reaches a predetermined value. According to the secondprior art, further, a laser beam is synthesized with a detection beambeforehand and the detection beam transmitted through an aperture isdetected when the aperture is drilled by irradiating the laser beam to aworkpiece whereby to stop the drilling of the aperture when the powertransmitted therethrough reaches a predetermined value.

[0010] As set forth above, according to the conventional laser beammachining methods, the depth of apertures to be drilled is controlled sothat the remain thickness is secured uniformly by detecting a smallquantity of laser beam or detection beam transmitted through the cutpart (aperture) of the workpiece. Therefore, a sensor for detecting thelaser beam or the detection beam is needed to be provided on asupporting member such as a jig for supporting a workpiece to besubjected to machining and in a position corresponding to a laser nozzlein such a manner that the sensor is movable integrally with theworkpiece on the opposite side of the workpiece, and this makes thedetection device not only complicated in construction but alsoexpensive. The problem in this case is that the necessity of adjustingthe detection level before the workpiece is subjected to machining makesit troublesome to detect slight variation in the thickness of theworkpiece. According to the first prior art, moreover, there is thepossibility that as the laser beam is transmitted through the apertureof the workpiece, a small hole or a scar is bored or left in the base ofthe aperture in the form of a tearable portion.

[0011] Further, in order to make constant the remain thickness, theoutput power of the laser beam has to be stabilized. For thestabilization of the laser beam, various factors or conditions such asthe voltage supplied to the oscillator of a laser beam machiningapparatus, the temperature of cooling water in an optical system and theambient temperature of the machining apparatus also have to be definite.Actually, these factors and conditions are hardly kept constant and withthe change of the optical system with time, moreover, the actual outputpower of the laser beam tends to vary in most cases.

[0012] In case where laser beam machining is carried out while theoutput power of the laser beam remains variable, the remain thickness ofa workpiece also varies and this may result in impeding development ofcleavage when the air bag is inflated, thus making small holes orleaving scars in the workpiece because a laser beam is allowed to passthrough the workpiece.

[0013] In order to compensate for the variable output power of the laserbeam, there has been proposed the art described in, for example,Japanese Patent Laid-Open No. 278687/1988 (the third prior art). In thisprior art, the output power of a pulsed laser beam following a referencepulse oscillated at a predetermined fundamental frequency as shown inFIG. 12 is detected pulse-to-pulse and the output power is integrated byan integration circuit. Then the integrated value is compared with areference value whereby to decide the error therebetween.

[0014] However, though discharge time is required for the integrationcircuit when the output of the pulsed laser beam is integrated, thedischarge time is difficult to secure because the output OFF time of thepulsed laser beam oscillated at a high speed of 5 KHz, for example, istoo short.

[0015] Therefore, it is conceivable to shorten the time constant of theintegration circuit but as is obvious from an integral value 30 of FIG.12, the oscillation noise of the pulsed laser beam is detected. In casewhere the time constant is set longer, on the other hand, the dischargetime of the integration circuit would not be secured as stated above.Consequently, a value widely different from the actual output powervalue is monitored and the laser output power cannot be detectedaccurately according to the prior art method. When the prior art methodis applied to forming a tearable portion in the instrument panel, itbecomes impossible to control the laser output power and this results indifficulty in making constant the remain thickness of the panel.

SUMMARY OF THE INVENTION

[0016] A first object of the invention made with a special attentiondirected to the foregoing problems existing in the prior art is toprovide a laser beam machining apparatus for ensuring that slightvariation in the thickness of a workpiece is made detectable by adetection device which is simple in construction and producible lesscostly and for accurately drilling perforations in a panel while theremain portion of the panel base secures the predetermined thickness,and a laser beam machining method therefor.

[0017] Further, a second object of the invention is also to provide alaser beam machining apparatus for making constant the remain thicknessof a panel base by allowing the value of a laser beam by pulseoscillation to be accurately securable and a laser beam machining methodtherefor.

[0018] In order to accomplish the first object, according to a firstaspect, there is provided a laser beam machining apparatus for forming ablind hole in a workpiece by the irradiation of a laser beam from anozzle to a rear surface of the workpiece while moving a machining headhaving the nozzle and the workpiece relatively, comprising:

[0019] a workpiece support member made of conductive material forsupporting and fixing the workpiece;

[0020] a distance detection unit provided in the machining head anddetecting the electrostatic capacity of a distance with a surface of theworkpiece support member as a reference; and

[0021] a control unit controlling the laser beam in response to theelectrostatic capacity which varies along with the thickness of theworkpiece disposed between the workpiece support member and the distancedetection unit.

[0022] Therefore, according to the first aspect of the invention, adetection device simple in construction is producible less costlycontrary to the prior art in which the laser beam or detection beamtransmitted through the blind hole of the workpiece is detected.Moreover, it is not only ensured to make detectable slight variation inthe thickness of the workpiece but also possible to accurately form theblind hole while the predetermined remain thickness of the bottom faceof the panel base is secured.

[0023] According to a second aspect of the invention, in the laser beammachining apparatus according to the first aspect, the laser outputpower by pulse oscillation is controlled in response to variation in theelectrostatic capacity while the nozzle and the workpiece are movedrelatively with a predetermined distance between the workpiece supportmember and the distance detection unit being made constant.

[0024] Therefore, according to the second aspect, the depth of thedrilling hole can be adjusted easily and accurately by setting thenumber of oscillated pulses of the laser beam in response to variationin the electrostatic capacity. Further, many perforations are formableat the predetermined intervals while the predetermined remain thicknessof the panel base is secured, which is fit for use in providing anopening for an air bag in an instrument panel for covering the air bag.

[0025] According to a third aspect of the invention, in the laser beammachining apparatus according to the first aspect, the distancedetection unit is provided to the nozzle.

[0026] Therefore, according to the invention described in the thirdaspect, no special mount need not be provided for the distance detectionunit, which is made simple in construction, whereby the accessibility ofthe nozzle to the workpiece is improved.

[0027] According to a fourth aspect of the invention, there is provideda laser beam machining method for forming a blind hole in a workpiece byirradiating a laser beam from a nozzle to a rear surface of theworkpiece while moving a machining head having the nozzle and theworkpiece relatively, comprising the steps of:

[0028] fixing the workpiece to a workpiece support member made ofconductive material;

[0029] detecting the electrostatic capacity of a distance with a surfaceof the workpiece support member as a reference; and

[0030] controlling the laser output power by pulse oscillation inresponse to the electrostatic capacity which varies along with thethickness of the workpiece disposed on the workpiece support member, sothat the bottom portion of the hole has a predetermined thickness.

[0031] Therefore, the same function as what is described in the firstaspect can be retained according to the invention described in thefourth aspect.

[0032] According to the fifth aspect of the invention, the laser beammachining method according to the fourth aspect, further comprises thestep of:

[0033] performing a peripheral groove by oscillating pulsesintermittently at predetermined intervals when the machining head andthe workpiece are moved relatively.

[0034] Therefore, the same function as what is described in the secondaspect can be retained according to the invention described in the fifthaspect.

[0035] According to the sixth aspect of the invention, the laser beammachining method according to the fourth aspect, further comprises thestep of:

[0036] adjusting the drilling depth by controlling the laser outputpower in response to the number of pulses of the laser output by pulseoscillation.

[0037] Further, in order to accomplished the second object, according toa seventh aspect of the invention, there is provided a laser beammachining apparatus of irradiating a laser beam by pulse oscillationfrom a nozzle to a rear surface of a workpiece while moving the nozzleand the workpiece relatively, so that blind holes are lined up in theworkpiece with remain portions in a front surface side of the workpiece,comprising:

[0038] a thickness detection unit detecting the thickness of theworkpiece,

[0039] an output power control unit controlling the output power of thelaser beam in response to the result detected by the thickness detectionunit so that the irradiation of the large power laser beam is switchedto the irradiation of a small power laser beam after the irradiation ofthe large power laser beam at each perforation;

[0040] a laser beam detection unit detecting the actual output power ofthe laser beam when the large power laser beam is irradiated,

[0041] an adder adding the output power detected by the laser beamdetection unit; and

[0042] an adjusting unit adjusting the output power of the small powerlaser beam irradiated after the irradiation of the large power laserbeam to conform to a command value in response to the result added bythe adder.

[0043] Therefore, according to the seventh aspect of the invention,machining blind holes with the remain portion can be formed in theworkpiece for machining the tearable portion by the irradiation of thelaser beam by pulse oscillation. Then the machining blind holes arecontinuously lined up in the form of the tearable portion along thesurface of the workpiece so as to form a groove-like tearable portion.In this case, the small power laser beam by pulse oscillation is used tomachine the blind holes after the large power laser beam thereby is usedto machine the blind holes and the number of pulses of the small powerlaser beam is so adjusted as to conform to the command value inaccordance with the laser beam output by the large power laser beam.Consequently, even though an error in the depth of the blind hole ismade because of the large power pulsed laser beam, the error can berectified at the time of drilling a hole by means of the small powerlaser beam, so that the remain thickness of the bottom face of the blindhole is uniformized. As the small power laser beam is used to drillholes after the large power laser beam is used to drill holes, theopening side of each hole is widely formed. Hence, inactive gas andswarfs of the workpiece are smoothly discharged, whereby the drillingoperation can be performed precisely and efficiently. In making adecision on the laser beam output power, further, the actual outputpower can be accurately calculated only by adding the pulse-to-pulsepower of the laser beam by pulse oscillation. On the basis of theaccurate power value, the drilling depth, that is, the accurate remainthickness of the panel base can be secured. Moreover, the depth of theblind holes is made adjustable by adjusting the laser beam output powerby pulse oscillation in response to the thickness of the workpiece andeven though the thickness of the workpiece varies, the uniform thicknessof the remain portion of the panel base can be secured.

[0044] According to an eighth aspect of the invention, in the laser beammachining apparatus according to the seventh aspect, the thicknessdetection unit includes an electrostatic capacity sensor provided at thefront end of the nozzle.

[0045] Therefore, in comparison with a case where the laser beamtransmitted through the workpiece is detected, it is ensured that thethickness of the workpiece is detectable without cause through-holes toappear in the workpiece. Moreover, the sensor is not needed to beinstalled on both sides of the workpiece and this makes the laser beammachining apparatus simple in construction.

[0046] According to a ninth aspect of the invention, in the laser beammachining apparatus according to the seventh aspect, the irradiationpower of the small power laser beam at each drilling is set in a rangebetween 70% or lower and 20% or higher of the irradiation power of thelarge power laser beam.

[0047] Therefore, in the invention described in the ninth aspect, sincethe small-output irradiation power is sufficiently lower than thelarge-output irradiation power, the depth of the blind hole is madeadjustable by the small power laser beam.

[0048] According to a tenth aspect of the invention, there is provided alaser beam machining method of irradiating a laser beam by pulseoscillation from a nozzle to a rear surface of a workpiece while movingthe nozzle and the workpiece relatively, so that blind holes are linedup in the workpiece with remain portions in a front surface side of theworkpiece, comprising the steps of:

[0049] detecting the thickness of the workpiece;

[0050] switching the irradiation of a large power laser beam to theirradiation of a small power laser beam after the irradiation of thelarge power laser beam at each perforation in response to the detectedresult of the thickness of the workpiece;

[0051] detecting the actual output power of the laser beam when thelarge power laser beam is irradiated;

[0052] adding the detected output power; and

[0053] adjusting the output power of the small power laser beamirradiated after the irradiation of the large power laser beam toconform to a command value in response to the added result.

[0054] Therefore, the same effect as what is described in the seventhaspect is achievable.

[0055] According to an eleventh aspect of the invention, in the laserbeam machining method according to the tenth aspect, the output power ofthe large power laser beam is corrected so that the output power thereofconforms to the command value in response to the added result.

[0056] Therefore, as the large power laser beam causing the drillingdepth to be great is an object for correction, the depth of the holescan effectively be corrected.

[0057] According to a twelfth aspect of the invention, in the laser beammachining method according to the tenth aspect, the irradiation power ofthe small power leaser beam at each perforation is set in a rangebetween 70% or lower and 20% or higher of the irradiation power of thelarge power laser beam.

[0058] Therefore, the same effect as what is described in the ninthaspect is achievable according to the invention described in the twelfthaspect.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059]FIG. 1 is a structural view of a laser beam machining apparatusaccording to a first embodiment of the invention;

[0060]FIG. 2 is a schematic view showing the laser beam machiningapparatus during the process of machining;

[0061]FIG. 3 is a perspective view showing a condition in which lasermachining is applied to the workpiece;

[0062]FIG. 4 is an explanatory view showing a condition in which outputpulses of a laser beam are controlled according to the first embodiment;

[0063]FIG. 5 is a characteristic view showing detection voltage ofelectrostatic capacity corresponding to the thickness of a workpiece;

[0064]FIG. 6 is a flowchart showing the operation of the laser beammachining apparatus of FIG. 1;

[0065]FIG. 7 is a structural view of a laser beam machining apparatusaccording to a second embodiment of the invention;

[0066]FIG. 8 is an explanatory view showing a condition in which blindholes are machined according to the second embodiment;

[0067]FIG. 9 is a diagram illustrating a signal for driving a laser beamby pulse oscillation according to the second embodiment;

[0068]FIG. 10 is a flowchart showing the operation of the laser beammachining apparatus according to the second embodiment;

[0069]FIG. 11 is a graph showing an added value of a large power laserbeam; and

[0070]FIG. 12 is a graph showing an integrated value of a laser beam ina conventional laser beam machining apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0071] <First Embodiment>

[0072] A first embodiment of the invention will now be described withreference to the drawings.

[0073] In a laser beam machining apparatus as shown in FIG. 1 accordingto the first embodiment of the invention, a support member 11 forming ajig made of conductive material is disposed on a table 10. The supportmember 11 is moved by a driving mechanism (not shown) in the directionsof X and Y. A workpiece 12 is disposed and fixedly supported on theupper surface of the support member 11 by air suction (not shown).According to this embodiment of the invention, the workpiece 12 is aninstrument panel used for covering an air bag (not shown) for anautomotive passenger seat as shown in FIG. 3.

[0074] As shown in FIGS. 1 and 2, a laser head 13 is driven by a motor(not shown) to be disposed opposite to the support member 11 andcontrolled so that it is movable close to and away from the supportmember 11 and also tiltable with respect thereto. Moreover, a lasernozzle 14 is projected from the lower portion of the laser head 13.Further, the support member 11 and the laser head 13 including the lasernozzle 14 are moved relatively in the directions of X and Y with apredetermined vertical distance L1 held therebetween, whereby the lasernozzle 14 is moved to a predetermined perforation position on theworkpiece 12.

[0075] A laser oscillator 15 is connected to the laser head 13 and alaser beam is irradiated from the laser oscillator 15 by pulseoscillation to the laser head 13 under the control of a control unit 16.Then the laser beam is guided to the laser nozzle 14 and irradiatedtherefrom intermittently at predetermined intervals onto the workpiece12. According to this embodiment of the invention, it has been arrangedthat a number of tearable portions 12 a such as blind holes are machinedby the laser beam in the workpiece 12. Consequently, a peripheral groove1 as a whole is formed on the workpiece 12 as shown in FIG. 3.

[0076] More specifically, as shown in FIG. 4 indicating W1 and W2 ofFIG. 2 in an enlarged manner, the control unit 16 oscillates and outputsa reference pulse with a predetermined frequency. And, the referencepulse is fed into the laser oscillator 15 and simultaneously on-offsignals are sent from the control unit 16 to the laser oscillator 15.According to the reference pulse and the on-off signals, a laser beamhaving the number of pulses P1, P2 corresponding to the widths W1, W2 ofthe ON signal is intermittently supplied from the laser oscillator 15 tothe laser head 13.

[0077] Therefore, the number of pulses P1 and that of pulses P2 areincreased or decreased respectively with the widths W1 and W2 of the ONsignal so as to control the laser output power. Moreover, the width ofone pulse and pulse-to-pulse distance of the laser beam is dependent onthe reference pulse. Since many pulses are oscillated in response to themoving rate of the laser nozzle 14 by setting the output pulse frequencyat as high as 5,000 Hz, for example, each of the widths W1 and W2 of theON signal acts as what is used to drill one hole. Thus, the tearableportions 12 a having depths L2 each corresponding to the number ofoutput pulses P1 and P2 are formed by the laser beam in the workpiece12.

[0078] The base of the laser nozzle 14 is formed of insulating materialand a first electrode 17 is formed on the inner peripheral face of thenozzle 14 by coating or the like, whereas a second electrode 18 issimilarly formed on the outer peripheral face thereof by coating or thelike. An electrostatic capacity sensor 19 as a detecting unit isconnected to the first electrode 17 and the second electrode 18. Wheneach blind hole 12 a of the workpiece 12 is formed, the electrostaticcapacity sensor 19 detects the electrostatic capacity between thesupport member 11 and the laser nozzle 14 and the detected result is fedinto the control unit 16. Although an electrostatic capacity sensor hasheretofore been utilized for measuring the distance quantity betweenmetallic materials, a non-metallic material has also been held betweenthe metallic materials in order to clarify the variation of theelectrostatic capacity therebetween from the thickness of non-metallicmaterial. In other words, as shown in FIG. 5, a detection voltage isobtained based on the electrostatic capacity corresponding to variationin the thickness of the workpiece 12.

[0079] An input unit 26 such as an input panel of FIG. 1 is intended tomanually input various kinds of data and commands.

[0080] A memory 20 is connected to the control unit 16 and stored withvarious kinds of data for use in controlling the laser oscillator 15 bymeans of the control unit 16. More specifically, the memory 20 stores,in the form of a table, for example, machining position data for theplurality of blind holes 12 a to be formed in the workpiece 12, relativedata on the detection voltage of the electrostatic capacity, the widthsW1 and W2 of the ON signal out of the on-off signals and the number ofoutput pulses P1 and P2. When the control unit 16 receives the detectedresult of the electrostatic capacity from the electrostatic capacitysensor 19 at the time each blind hole 12 a of the workpiece 12 is formedby laser beam machining, the control unit 16 sets the widths W1 and W2of the ON signal out of the on-off signals directed to the laseroscillator 15 according to the relative data stored in the memory 20.With this setting, the number of pulses P1 and that of pulses P2 of thelaser beam supplied from the laser oscillator 15 is changed, whereby theirradiation output power of the laser beam is so controlled as to beincreased or decreased.

[0081] As the thickness of the workpiece 12 in the machining positiondecreases, voltage of large electrostatic capacity is detected. On thebasis of the detection voltage, the widths W1 and W2 of the ON signalout of the on-off signals are set small and this results in outputting alaser beam having a smaller number of pulses P1, P2, so that blind holes12 a having a smaller depth L2 are formed. As the thickness of theworkpiece 12 in the machining position increases, on the contrary, thedetection voltage of a small electrostatic capacity is produced. On thebasis of the detection voltage, the widths W1 and W2 of the ON signalout of the on-off signals are set large and this results in outputting alaser beam having a greater number of pulses P1 or P2, so that blindholes 12 a having a greater depth L2 are formed. In other words, thedrilling depth L2 is adjusted by increasing or decreasing the number ofpulses. Consequently, even though the thickness of the workpiece 12varies, desired depth can be set to each blind hole 12 a, whereby it ispossible to secure the uniform remain thickness L3 of the panel base inthe workpiece.

[0082] Further, program data shown by a flowchart of FIG. 6, as will bedescribed below, is stored in the memory 20.

[0083] The operation of a laser beam machining apparatus as mentionedabove will now be described by reference to the flowchart of FIG. 6. Theprogram stored in the memory 20 is conducted under the control of thecontrol unit 16 as shown in the flowchart of FIG. 6.

[0084] When the laser beam machining is started in the laser beammachining apparatus, the laser nozzle 14 is moved to a programmedposition above the workpiece 12 on the support member 11 and disposed insuch a condition that a predetermined distance L1 is providedtherebetween (Step S1). Therefore, the distance between the laser nozzle14 and the support member 11 is kept having a specified value.

[0085] In this condition, the laser head 13 including the laser nozzle14 and the support member 11 used to support the workpiece 12 are movedrelatively, so that the laser beam machining of the workpiece 12 isstarted as shown in FIG. 3 (Step S2). In this case, the electrostaticcapacity sensor 19 detects electrostatic capacity in a condition thatthe position of the laser nozzle 14 corresponds to the machiningposition of one blind hole 12 a, and detection voltage corresponding tothe thickness of the workpiece 12 is fed into the control unit 16 (StepS3).

[0086] On the basis of the detection voltage of the electrostaticcapacity, the widths W1 and W2 of the ON signal out of the on-offsignals directed to the laser oscillator 15 from the control unit 16 areset. Therefore, the number of pulses P1 and that of pulses P2 of thelaser beam supplied from the laser oscillator 15 are set in response tothe respective widths W1 and W2 of the ON signal (Step S4). Further, thelaser beam having the set number of pulses P1, P2 sent from the laseroscillator 15 is irradiated from the laser nozzle 14 to the workpiece12, whereby the blind holes 12 a are formed while the predeterminedremain thickness of the panel base is secured (Step S5). In this case,the greater the number of pulses P1 and that of pulses P2, the deeperthe holes are formed, whereas the smaller the number of pulses P1 andthat of pulses P2, the shallower the holes are formed. In case where thedetected thickness of each hole 12 a is great, control is performed sothat the set values of the number of pulses P1 and that of pulses P2increases, whereas in case where the detected thickness thereof issmall, control is performed so that the set values of the number ofpulses P1 and that of pulses P2 decreases. Consequently, the remainthickness L3 of the panel base in the workpiece 12 is kept constant.

[0087] Upon termination of formation of each blind hole 12 a in theworkpiece 12, whether or not the presence of the next blind hole 12 a inthe machining position data is decided (Step S6). In making thisdecision, Step S3 is followed again when the next blind hole 12 a existsand the operation at Steps S3 to S6 is repeated whereby to form aplurality of blind holes 12 a in the workpiece 12 with the predeterminedremain thickness L3 being secured at the predetermined intervals. Whenthe next blind hole 12 a is absent in the machining position data, thelaser-beam operation with respect to one workpiece 12 is terminated(Step S7).

[0088] Therefore, the following effect is obtained according to thisembodiment of the invention.

[0089] In this laser beam machining apparatus, the workpiece 12 isfixedly supported on the support member 11 made of conductive materialwhen the tearable portions 12 a are formed at the predeterminedintervals in the workpiece 12 by irradiating the laser beam from thelaser nozzle 14 thereto. In this condition, the electrostatic capacitysensor 19 detects the electrostatic capacity between the support member11 and the laser nozzle 14. On the basis of the detected results, thecontrol unit 16 performs controlling of the radiation output power ofthe laser beam from the laser nozzle 14 so that the laser output powerthereof is varied each time one blind hole 12 a is formed.

[0090] Accordingly, the provision of the detector on the side of thesupport member 11 can be dispensed with contrary to the prior art inwhich the laser beam or detection beam transmitted through the tearableportion 12 a of the workpiece 12 is detected, whereby a detection devicesimple in construction is producible less costly. Moreover, it is notonly ensured to make detectable slight variation in the thickness of theworkpiece 12 but also possible to accurately form tearable portions in apanel while the predetermined remain thickness L3 is secured. Moreover,any scar is never left in the workpiece 12 since no transmitted lightfor detection is needed to be generated.

[0091] In this laser beam machining apparatus, the irradiation outputpower of the laser beam controlled by the control unit 16 depends on thenumber of pulses P1 or P2. In other words, since the number of pulses P1and that of pulses P2 of the laser beam are variably set according tothe detected results of electrostatic capacity, the tearable portions 12a can accurately be formed with the predetermined remain thickness L3being secured.

[0092] In this laser beam machining apparatus, a panel for covering anautomotive air bag has been referred to as the workpiece 12. Therefore,the external appearance is restrained from being spoiled when thetearable portions 12 a are formed at the predetermined intervals in therear of the panel used to cover the air bag because small holes or scarsare left in the surface side of the panel. Thus, a high-quality panelcan be provided.

[0093] <Modified Examples of the First Embodiment>

[0094] The following modification can be made to the first embodiment ofthe invention.

[0095] According to the first embodiment of the invention, the number ofoutput pulses P1 or P2 as the irradiation output power of the laser beamcontrolled by the control unit 16 is set changeable. On the other hand,the output power or output frequency of a laser beam as the irradiationoutput power of the laser beam is set changeable instead of the numberof output pulses.

[0096] According to the first embodiment of the invention, moreover, theworkpiece 12 subjected to the laser beam machining is an instrumentpanel for covering the air bag of an automobile. On the other hand, theinvention is applied to forming grooves in a panel for covering an airbag to be incorporated in a steering wheel or any industrial materialother than an instrument panel free from machining scars left in itssurface.

[0097] According to the first embodiment of the invention, machiningposition data on the plurality of blind holes 12 a, relative data on thedetection voltage of the electrostatic capacity, the widths W1 and W2 ofthe ON signal out of the on-off signals and the number of output pulsesP1 and P2 are stored in the form of a table. Further, these items ofdata are sequentially read out whereby to set the number of outputpulses intended for each blind hole 12 a. On the other hand, instead ofthis, the number of output pulses for each blind hole 12 a is arrangedso that it is computed in accordance with the level of the detectionvoltage of the electrostatic capacity.

[0098] According to the first embodiment of the invention, the laserbeam has been irradiated intermittently to the workpiece so as to securepanel strength. However, a peripheral groove is formed by irradiating alaser beam continuously depending on the machining purpose.

[0099] The same effect as what is achievable according to the firstembodiment of the invention is also obtainable even when thearrangements as stated above are additionally made.

[0100] <Second Embodiment>

[0101] A second embodiment of the invention will now be described withreference to the drawings.

[0102]FIG. 7 shows a laser beam machining apparatus according to thesecond embodiment. Since respective constructions of a support member 11forming a jig and a laser head 13 are substantially identical with thoseof the first embodiment, these detailed descriptions are omitted in thisembodiment. Further, a workpiece 12 to be machined is an instrumentpanel shown in FIGS. 2 and 3 as well as the first embodiment.

[0103] As shown in FIG. 7, a laser oscillator 15 is connected to thelaser head 13. A plurality of mirrors 21 to 23 and a focusing lens 14 aare disposed between the laser oscillator 15 and the laser nozzle 14, sothat a laser beam path is formed between the laser head 13 and the laseroscillator 15. One of the mirrors 21 to 23 is used as a half mirror 21and part of the laser beam is passed through the half mirror. Adetection sensor 24 as a laser beam detection unit is disposed on anoptical transmission path and the actual output power of a laser beam bypulse oscillation from the laser oscillator 15 is detected.

[0104] The laser oscillator 15 is electrically connected to a controlunit 16. The control unit 16 controls the operation of the whole laserbeam machining apparatus, to say nothing of the laser oscillator 15. Amemory 20 is connected to the control unit 16 and stored with variouskinds of data and programs. The control unit 16 and the memory 20 form acorrection unit, an adjusting unit and an output power control unit.Under the control of the control unit 16 according to the various kindsof data and programs stored in the memory 20, the laser beam is suppliedfrom the laser oscillator 15 to the laser head 13 and irradiated to theworkpiece 12. Accordingly, blind holes 12 a are formed by the laser beamso that the workpiece 12 has a predetermined remain thickness L3 asshown in FIG. 8. When the laser head 13 and the workpiece 12 are movedrelatively in the directions of X and Y, a plurality of blind holes 12 aare continuously formed along the surface of the workpiece 12 and byforming the continuous cut parts intermittently, a tearable portion inthe form of perforations is formed in the workpiece 12.

[0105] More specifically, as shown in FIG. 9, a reference pulse having afundamental frequency of (e.g., 5 KHz), an ON signal, an OFF signal anda switching signal are supplied from the control unit 16 to the laseroscillator 15. When the ON signal is output, the laser oscillator 15oscillates a continuous pulsed large power beam in accordance with thereference pulse. When the switching signal is output, the oscillatedlaser beam is switched to the small power laser beam at a predeterminedratio to the large power laser beam. According to this embodiment of theinvention, the small-output power is 50% of the large-output power. Whenthe OFF signal is output, the laser beam output by small-output pulseoscillation is stopped. The number of pulses of the large power laserbeam and that of the small power laser beam are set beforehand. However,the number of pulses of the large power laser beam and that of the smallpower laser beam are, as will be described later, set or changeddifferently under the control of the control unit 16.

[0106] The laser beam detection sensor 24 is used to detect the outputpower of the large power laser beam. Further, the control unit 16computes drilling depth per pulse of the large power laser beamaccording to the detected output power of the large power laser beam.

[0107] On the other hand, the control unit 16 is provided with an adder25, into which the output power of a large power laser beam detected bythe detection sensor 24 is added, and the added value is stored in thememory 20. Further, the control unit 16 adjusts the output timing of theOFF signal according to the result of the output added by the adder 25.Consequently, the output value of a small power laser beam following theoutput power of the large power laser beam is corrected by adjusting theoutput timing of the OFF signal. According to this embodiment of theinvention, the output value of the small power laser beam includes atleast one of the pulse frequency of the laser beam, peak power of eachpulsed laser beam and the number of pulses.

[0108] As well as the first embodiment, the control unit 16 adjusts theoutput timing of a switching signal based on the detected results of anelectrostatic capacity sensor 19 as shown in FIG. 6. As will bedescribed below, according to the second embodiment of the invention,the depth of about 80% of blind hole is defined by the large power laserbeam, whereas the depth of the rest is defined by the small power laserbeam. Consequently, the output power of the large power laser beam isset in response to the thickness of the workpiece 12. Moreover, thecontrol unit 16 adjusts the output timing of the switching signal foruse in drilling the following hole on the basis of a drilling quantityper pulse of the large power laser beam as well as the value added bythe adder 25 whereby to correct the value of the following large powerlaser beam by pulse oscillation. According to this embodiment of theinvention, the output value of the large power laser beam includes atleast one of the pulse frequency of the laser beam, peak power of eachpulsed laser beam and the number of pulses.

[0109] A thermoelectric power monitor 27 is disposed in one cornerportion of the support member 11. The thermoelectric power monitor 27 isused to measure the intensity of the laser beam on receiving theirradiation of the laser beam before the start of machining and duringthe work arrangements are made. The control unit 16 receives detectionsignals from the thermoelectric power monitor 27 and decides thedifference between the command value of intensity of the laser beam andthe actual output power value of the intensity thereof. Further, thecontrol unit 16 adjusts the output power level of the pulse-to-pulselaser beam according to the decision so that the output power level ofthe actual intensity becomes closer to the command value.

[0110] An input unit 26 such as an input panel of FIG. 7 is intended tomanually input various kinds of data and commands.

[0111] A description will now be given of a laser beam machining methodthrough the operation of the laser beam machining apparatus thusconfigured according to the second embodiment of the invention byreference to a flowchart of FIG. 10. The flowchart of FIG. 10 proceedsby executing the program stored in the memory 20 under the control ofthe control unit 16.

[0112] When the laser beam machining is started, the laser nozzle 14 ismoved to a programmed position above the workpiece 12 on the supportmember 11 and disposed in such a condition that a predetermined distanceL1 is provided therebetween (Step S101). Therefore, the distance betweenthe laser nozzle 14 and the support member 11 is kept having a specificvalue.

[0113] In this condition, the laser head 13 including the laser nozzle14 and the support member 11 used to support the workpiece 12 are movedrelatively in the directions of X and Y, so that the laser beammachining of the workpiece 12 is started (Step S102). In this case,electrostatic capacity is detected first by the electrostatic capacitysensor 19 while the position of the laser nozzle 14 corresponds to themachining position of one hole 12 a and detection voltage correspondingto the thickness of the workpiece 12 is fed into the control unit 16(Step S103).

[0114] On the basis of the detection voltage of the electrostaticcapacity, the output power of the large power laser beam, that is, thenumber of pulses, for example, out of the output powers of the laserbeam by pulse oscillation is set and corrected by the control unit 16(Steps S104 and S105). At this time, the number of pulses of the smallpower laser beam is predetermined. In other words, the number of pulsesof the large power laser beam is set in response to the thickness of theworkpiece 12 detected by the electrostatic capacity sensor 19 so thatthe remain thickness L3 of the panel base becomes constant at Steps S104and S105 as is obvious from FIG. 8. Incidentally, according to thisembodiment of the invention, a drilling ratio is pre-set at standardvalues such that blind holes are machined by means of the large powerlaser beam to the extent of 80% of the drilling depth and machined bymeans of the small power laser beam to the extend of 20% thereof.

[0115] Then the control unit 16 outputs an ON signal shown in FIG. 9 andthe large power laser beam by pulse oscillation having the number ofreference pulses at the fundamental frequency is irradiated to thedrilling position of the workpiece 12 (Step S106) whereby to start theoperating of machining a blind hole (see FIGS. 8 and 11). When the largepower laser beam is irradiated, the output (power) is detected by thelaser beam detection sensor 24 (Step S107) and the value of the outputpower thus detected is added by the adder 25 with time, a value 31resulting from the addition is stored as shown in FIG. 11 (Step S108).

[0116] When laser machining by a set large power pulsed laser beam bypulse oscillation is thus terminated (Step S109), the total output valueof the actual large power laser beam additionally computed by the adder25 is compared with a total output power value to be obtained by the setlaser beam, that is, the command value (Step S110). In case where theactual output power is found insufficient as the result of comparison,the command output of the next small power laser beam is so adjusted asto be increased with the respect to the set value, whereas in case wherethe actual output power is found too great, the command output is soadjusted as to be decreased (Step S111). In case where both output powervalues are equal, the set value is maintained without being adjusted.

[0117] Further, small power laser beam machining with the number ofpulses set at Step S111 is carried out (Step S112) and when the numberof pulses reaches the set number, the operation of machining aperforation 12 a is terminated (Step S113). Therefore, the machiningoperation by means of the small power laser beam is stopped when thepredetermined remain thickness L3 of the panel base is attained in theworkpiece 12.

[0118] Subsequently, the presence or absence of a hole to be machined isdecided (Step S114). In the absence of a hole to be machined next, thelaser beam machining is stopped (Step S116). The adder 25 causes thestored charge to be discharged as shown in FIG. 11 by utilizing timeupon termination of machining so as to provide for the next addition. Inthe presence of a hole to be machined next, the drilling depth per pulseof the large power laser beam is calculated (Step S115).

[0119] Then, the routine returns to Step S103 at which the thickness ofthe workpiece 12 is detected by electrostatic capacity sensor 19, sothat the number of pulses by means of the large power pulsed laser beamis calculated to correspond to the thickness. At this time, thecalculation of the number pulses is performed based on drilling depthper pulse calculated at Step S115. In other words, the number of pulsesof the large power pulsed laser beam is calculated so that the valueobtained by multiplying the drilling depth per pulse by the number ofpulses corresponds to that of the drilling depth attained by the largepower pulsed laser beam, and the calculated number thereof is correctedwhen necessary.

[0120] Then the routine at Step S103 and the following steps isimplemented. As the routine is repeated, a plurality of blind holes 12 aare continuously made along the surface of the workpiece 12 and thecontinuous portions are intermittently formed, whereby a tearableportion 1 in a desired form can be provided in the surface of theworkpiece 12 as shown in FIG. 3.

[0121] Therefore, according to the second embodiment of the invention,the following effect is achievable.

[0122] The correction of the output power of the laser beam is made atthe time of small power laser irradiation following the large powerlaser irradiation. Even though an error in the drilling depth of thehole is made because of the large power pulsed laser beam, the error canbe rectified at the time of machining by means of the small power laserbeam. Consequently, it is possible to accurately secure thepredetermined remain thickness L3 of the panel base, whereby to form thetearable portion 1 that is surely opened under the predeterminedconditions.

[0123] Since the drilling operation is carried out by means of the largepower laser beam prior to the drilling operation by means of the smallpower laser beam, the opening side of the blind holes 12 a is widelyformed. Consequently, inactive gas and swarfs of the workpiece aresmoothly discharged from the blind holes 12 a at the time of irradiationof the laser beam, whereby the drilling operation can be performedprecisely and efficiently.

[0124] As the pulse-to-pulse output power of the laser beam by the pulseoscillation is added by the adder 25, the total power value of the laserbeam output by the pulse oscillation can accurately be calculated toaccurately secure the drilling depth, that is, the desired remainthickness of the panel base, which is different from the case of usingintegration.

[0125] By detecting the thickness of the workpiece 12 so as to adjustthe output power of the laser beam in response to variation in thethickness thereof, the depth of blind holes 12 a is made adjustable inresponse to the thickness of the workpiece 12, so that the remainthickness L3 of the panel base is kept constant.

[0126] When the laser beam is adjusted in response to the thickness ofthe workpiece 12, the number of pulses of the laser beam givenconsiderable deep in determining the drilling depth is made an objectfor adjustment by adjusting the output power of the large power laserbeam. Therefore, the drilling depth by means of laser beam machining caneffectively be corrected.

[0127] When the laser beam output power by the pulse oscillation isadjusted in response to the result of addition made by the adder 25, thedrilling depth can finely be adjusted by adjusting the number of smallpower laser beams, whereby the accurate remain thickness L3 of the panelbase is secured.

[0128] The laser beam output power by the pulse oscillation for thefollowing holes is corrected in response to the result of addition madeby the adder 25, whereby the constant remain thickness L3 of the panelbase is secured. Thus, the uniform remain thickness of the panel basecan be provided as a whole.

[0129] <Modified Examples of the Second Embodiment>

[0130] The following modification can be made to the second embodimentof the invention.

[0131] According to the second embodiment of the invention, the laserbeam output power for the following drilling operation is corrected bydetecting the output power of the large power laser beam. On the otherhand, instead of this, the output power of the large power laser beamand the output of the small power laser beam both may be detected andreflected on the following drilling operation, whereby more accuratedrilling operation can be carried out.

[0132] According to the second embodiment of the invention, the laseroutput power of the following large power laser beam is corrected bydetecting the output power of the large power laser beam. On the otherhand, instead of this, the output power of the small power laser beammay be corrected, whereby the drilling depth can finely be adjusted.

[0133] According to the second embodiment of the invention, the resultdetected by the electrostatic capacity sensor is reflected on the outputpower of the large power pulsed laser beam. On the other hand, theresult detected by the electrostatic capacity sensor may be reflected onthe small power pulsed laser beam.

[0134] According to the second embodiment of the invention, theirradiation power of the small power laser beam is reduced to 50% ofthat of the large power laser beam. On the other hand, the irradiationpower of the small power laser beam may be set at any value between 70%or lower and 20% or higher.

[0135] As a detection unit for detecting the thickness of the workpiece12, there may be used any sensor other than the electrostatic capacitysensor; for example, a sensor for mechanically detecting the thicknessof a workpiece by contacting the surface of the workpiece 12, wherebycost for such a detection unit is reducible.

[0136] The invention is applied to a case where laser machining isapplied any other component than an automotive instrument panel; forexample, the center cover of a steering wheel. Even in this case, thesame operation/working effect as what has been described in the secondembodiment of the invention is achievable.

[0137] While only certain embodiments of the invention have beenspecifically described herein, it will apparent that numerousmodifications may be made thereto without departing from the spirit andscope of the invention.

What is claimed is:
 1. A laser beam machining apparatus for drilling ablind hole in a workpiece by irradiating a laser beam from a nozzle to arear surface of the workpiece while moving a machining head having thenozzle and the workpiece relatively, comprising: a workpiece supportmember made of conductive material for supporting and fixing theworkpiece; a distance detection unit provided in the machining head anddetecting the electrostatic capacity of a distance with a surface of theworkpiece support member as a reference; and a control unit controllingthe laser beam in response to the electrostatic capacity which variesalong with the thickness of the workpiece disposed between the workpiecesupport member and the distance detection unit.
 2. The laser beammachining apparatus according to claim 1, wherein the laser output powerby pulse oscillation is controlled in response to variation in theelectrostatic capacity while the nozzle and the workpiece are movedrelatively with a predetermined distance between the workpiece supportmember and the distance detection unit being made constant.
 3. The laserbeam machining apparatus according to claim 1, wherein the distancedetection unit is provided to the nozzle.
 4. The laser beam machiningapparatus according to claim 3, wherein the distance detection unitincludes a first electrode formed on an inner peripheral face of thenozzle made of insulating material; a second electrode formed on anouter peripheral face of the nozzle; and an electrostatic capacitysensor electrically connected to the first electrode and the secondelectrode.
 5. A laser beam machining method for forming a blind hole ina workpiece by irradiating a laser beam from a nozzle to a rear surfaceof the workpiece while moving a machining head having the nozzle and theworkpiece relatively, comprising the steps of: fixing the workpiece to aworkpiece support member made of conductive material; detecting theelectrostatic capacity of a distance with a surface of the workpiecesupport member as a reference; and controlling the laser output power bypulse oscillation in response to the electrostatic capacity which variesalong with the thickness of the workpiece disposed on the workpiecesupport member, so that the bottom portion of the hole has apredetermined thickness.
 6. The laser beam machining method according toclaim 5, further comprising the step of: performing a peripheral grooveby oscillating pulses intermittently at predetermined intervals when themachining head and the workpiece are moved relatively.
 7. The laser beammachining method according to claim 5, further comprising the step of:adjusting the drilling depth by controlling the laser output power inresponse to the number of pulses of the laser output by pulseoscillation.
 8. A laser beam machining apparatus of irradiating a laserbeam by pulse oscillation from a nozzle to a rear surface of a workpiecewhile moving the nozzle and the workpiece relatively, so that blindholes are lined up in the workpiece with remain portions in a frontsurface side of the workpiece, comprising: a thickness detection unitdetecting the thickness of the workpiece, an output power control unitcontrolling the output power of the laser beam in response to the resultdetected by the thickness detection unit so that the irradiation of thelarge power laser beam is switched to the irradiation of a small powerlaser beam after the irradiation of the large power laser beam at eachdrilling; a laser beam detection unit detecting the actual output powerof the laser beam when the large power laser beam is irradiated, anadder adding the output power detected by the laser beam detection unit;and an adjusting unit adjusting the output power of the small powerlaser beam irradiated after the irradiation of the large power laserbeam to conform to a command value in response to the result added bythe adder.
 9. The laser beam machining apparatus according to claim 8,wherein the thickness detection unit includes an electrostatic capacitysensor provided at the front end of the nozzle.
 10. The laser beammachining apparatus according to claim 8, wherein the thicknessdetection unit includes a first electrode formed on an inner peripheralface of the nozzle made of insulating material; a second electrodeformed on an outer peripheral face of the nozzle; and an electrostaticcapacity sensor electrically connected to the first electrode and thesecond electrode, and the thickness of the workpiece is calculated basedon the detection result obtained from the electrostatic capacity sensor.11. The laser beam machining apparatus according to claim 8, wherein theirradiation power of the small power laser beam at each blind hole isset in a range between 70% or lower and 20% or higher of the irradiationpower of the large power laser beam.
 12. A laser beam machining methodof irradiating a laser beam by pulse oscillation from a nozzle to a rearsurface of a workpiece while moving the nozzle and the workpiecerelatively, so that blind holes are lined up in the workpiece withremain portions in a front surface side of the workpiece, comprising thesteps of: detecting the thickness of the workpiece; switching theirradiation of a large power laser beam to the irradiation of a smallpower laser beam after the irradiation of the large power laser beam ateach drilling in response to the detected result of the thickness of theworkpiece; detecting the actual output power of the laser beam when thelarge power laser beam is irradiated; adding the detected output power;and adjusting the output power of the small power laser beam irradiatedafter the irradiation of the large power laser beam to conform to acommand value in response to the added result.
 13. The laser beammachining method according to claim 12, wherein the output power of thelarge power laser beam is corrected so that the output power thereofconforms to the command value in response to the added result.
 14. Thelaser beam machining method according to claim 12, wherein theirradiation power of the small power leaser beam at each drilling is setin a range between 70% or lower and 20% or higher of the irradiationpower of the large power laser beam.